The present invention relates to a photographic macro lens system. More particularly the present invention relates to a compact macro lens system that employs a floating mechanism with the overall lens system being divided into two groups, and in which the distance between the retrofocus first group and the second group is adjusted to ensure good performance over a wide shooting range including a life-size shot.
Conventional photographic lens systems are designed to perform aberrational compensation using an infinite distance as a reference. On the other hand macro lens systems adopt a close distance as a reference for aberrational compensation. Macro lens systems are also frequently used in ordinary photographic shooting in which achieving effective aberrational compensation over a wide shooting range from the closest distance to infinity is desired. In response to this need, some macro lens systems enable shooting over a wide range including a life-size shot (1 x) by adopting a floating mechanism, e.g., the systems described in JP-A-No. 59-228220 and JP-A-No. 62-195617 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). A macro lens system employing a retrofocus first lens group is described in JP-No. 62-160412.
The adoption of a floating mechanism has been successful to some extent in solving the problem on account of the change in shooting distance. However, this approach suffers disadvantages that are inherent to the floating mechanism such as the need to divide the overall lens system into three groups.
A macro lens system employing a retrofocus first group does not completely perform efficient aberrational compensation. In other words, in response to a change in the shooting distance from infinity to life size the system will experience great variations in aberration and in particular astigmatism.